1. Field of the Invention
The present invention relates to a process for electrolytically purifying a photographic developer waste solution, thereby easily and sufficiently degrading as well as removing from such a waste solution those components having high COD (chemical oxygen demand) concentrations.
2. Description of the Prior Art
Color photography is gaining wide acceptance among consumers and plates for photoprinting are being manufactured at a high rate, so large quantities of photographic developer waste solution must be discharged, and it is ecologically very objectionable to dump them into the waterways without due treatment thereof, for they contain in as much as tens of thousands of ppm those components which are high in COD levels and therefore prove to be pollutants to the water courses into which they are dumped. In addition, with the regulations on environmental pollutions being applied more rigorously in recent years, the removal of such pollutants from photographic developer waste solutions has become a matter of immediate attention.
The conventional techniques of purifying a photographic developer waste solution are twofold: one is thermal oxidative decomposition using hypochlorite as an oxidizing agent, and the other is an activated sludge process. The former, however, is disadvantageous in that it needs a long heating time, involves complicated procedures such as the control of the amount of agents to be used, and lastly, requires expensive agents, whereas in the latter, not only is large-scale equipment necessary including a pool for the waste solution but processing time is also inevitably increased. Neither method is successful in removing objectionable components of high COD values, because they leave behind components having COD concentrations of the order of 100 ppm and necessitate such secondary treatments as neutralization, precipitation, filtration or combustion, dilution and so forth. These additional steps cannot be taken without involving an increase in operating costs of the conventional processes. What is more, a recent method of adding salt (sodium chloride) to waste water including organic substances and effecting electrolysis to remove those components which have high COD values from the waste water is found to be impractical in sufficient removal of such objectionable components, for at the lower levels of COD, electrolysis becomes very difficult to carry out. Under such conditions, none of the predecessors of the present invention have succeeded in relying upon electrolytic oxidation alone for removing high concentrations of COD levels from the developer waste solution.